The present invention is directed to an expansion anchor assembly to be secured in a borehole and comprises an expansion sleeve and an anchor rod. The expansion sleeve includes a plurality of shell-shaped expansion sections extending from the leading end of the sleeve toward its trailing end. The expansion sections are spaced apart in the circumferential direction by axially extending slots. By drawing an expansion cone on the end of the anchor rod into the expansion sleeve, the expansion sections can be deflected radially outwardly by bending at a weakened section located between circumferentially extending radially inner and radially outer recesses.
An expansion anchor assembly to be fastened in boreholes with a conical widening is disclosed in U.S. Pat. No. 4,519,753. The expansion anchor assembly includes an expansion sleeve with shell-shaped expansion sections and an anchor rod with an expansion cone. The expansion sections are deflected radially outwardly by drawing the expansion cone into the conical widening of the boreholes to form a positive-locking engagement. In deflecting the expansion sections, they are bent around a weakened section which connects them to an adjacent portion of the expansion sleeve.
The weakened section is formed by inner and outer recesses in the form of grooves extending in the circumferential direction of the expansion sections. The weakened sections comprise a cross-sectional configuration in axial projection shaped as a circular arc. Such a configuration is distinguished, based on the known strength of materials, by a high moment of resistance. Consequently, high forces are required to achieve the deflection of the expansion sections and such forces are introduced as radial forces in the region of the borehole wall adjoining the conically widened part and opposite to the insertion direction of the assembly. Such forces can damage this region of the receiving material containing the borehole and, as a result, impair the anchorage of the expansion anchor assembly.